Pitch-based carbon foam and composites

ABSTRACT

A process for producing carbon foam or a composite is disclosed which obviates the need for conventional oxidative stabilization. The process employs mesophase or isotropic pitch and a simplified process using a single mold. The foam has a relatively uniform distribution of pore sizes and a highly aligned graphic structure in the struts. The foam material can be made into a composite which is useful in high temperature sandwich panels for both thermal and structural applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/136,596, filed Aug. 19, 1998, which is a divisional application ofU.S. patent application Ser. No. 08/921,875, filed Sep. 2, 1997, nowU.S. Pat. No. 6,033,506.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government has rights in this invention pursuant tocontract No. DE-AC05-00OR22725 between the United States Department ofEnergy and UT-Battelle, LLC.

BACKGROUND OF THE INVENTION

The present invention relates to carbon foam and composites, and moreparticularly to a process for producing them.

The extraordinary mechanical properties of commercial carbon fibers aredue to the unique graphitic morphology of the extruded filaments. SeeEdie, D. D., “Pitch and Mesophase Fibers,” in Carbon Fibers, Filamentsand Composites, Figueiredo (editor), Kluwer Academic Publishers, Boston,pp. 43-72 (1990). Contemporary advanced structural composites exploitthese properties by creating a disconnected network of graphiticfilaments held together by an appropriate matrix. Carbon foam derivedfrom a pitch precursor can be considered to be an interconnected networkof graphitic ligaments or struts, as shown in FIG. 1. As suchinterconnected networks, they represent a potential alternative as areinforcement in structural composite materials.

Recent developments of fiber-reinforced composites has been driven byrequirements for improved strength, stiffness, creep resistance, andtoughness in structural engineering materials. Carbon fibers have led tosignificant advancements in these properties in composites of variouspolymeric, metal, and ceramic matrices.

However, current applications of carbon fibers has evolved fromstructural reinforcement to thermal management in application rangingfrom high density electronic modules to communication satellites. Thishas simulated research into novel reinforcements and compositeprocessing methods. High thermal conductivity, low weight, and lowcoefficient of thermal expansion are the primary concerns in thermalmanagement applications. See Shih, Wei, “Development of Carbon-CarbonComposites for Electronic Thermal Management Applications,” IDAWorkshop, May 3-5, 1994, supported by AF Wright Laboratory underContract Number F33615-93-C-2363 and AR Phillips Laboratory ContractNumber F29601-93-C-0165 and Engle, G. B., “High Thermal Conductivity C/CComposites for Thermal Management,” IDA Workshop, May 3-5, 1994,supported by AF Wright Laboratory under Contract F33615-93-C-2363 and ARPhillips Laboratory Contract Number F29601-93-C-0165. Such applicationsare striving towards a sandwich type approach in which a low densitystructural core material (i.e. honeycomb or foam) is sandwiched betweena high thermal conductivity facesheet. Structural cores are limited tolow density materials to ensure that the weight limits are not exceeded.Unfortunately, carbon foams and carbon honeycomb materials are the onlyavailable materials for use in high temperature applications (>1600°C.). High thermal conductivity carbon honeycomb materials are extremelyexpensive to manufacture compared to low conductivity honeycombs,therefore, a performance penalty is paid for low cost materials. Highconductivity carbon foams are also more expensive to manufacture thanlow conductivity carbon foams, in part, due to the starting materials.

In order to produce high stiffness and high conductivity carbon foams,invariably, a pitch must be used as the precursor. This is because pitchis the only precursor which forms a highly aligned graphitic structurewhich is a requirement for high conductivity. Typical processes utilizea blowing technique to produce a foam of the pitch precursor in whichthe pitch is melted and passed from a high pressure region to a lowpressure region. Thermodynamically, this produces a “Flash,” therebycausing the low molecular weight compounds in the pitch to vaporize (thepitch boils), resulting in a pitch foam. See Hagar, Joseph W. and Max L.Lake, “Novel Hybrid Composites Based on Carbon Foams,” Mat. Res. Soc.Symp., Materials Research Society, 270:29-34 (1992), Hagar, Joseph W.and Max L. Lake, “Formulation of a Mathematical Process Model ProcessModel for the Foaming of a Mesophase Carbon Precursor,” Mat. Res. Soc.Symp., Materials Research Society, 270:35-40 (1992), Gibson, L. J. andM. F. Ashby, Cellular Solids: Structures & Properties, Pergamon Press,New York (1988), Gibson, L. J., Mat. Sci. and Eng A110, 1 (1989),Knippenberg and B. Lersmacher, Phillips Tech. Rev., 36(4), (1976), andBonzom, A., P. Crepaux and E. J. Moutard, U.S. Pat. No. 4,276,246,(1981). Then, the pitch foam must be oxidatively stabilized by heatingin air (or oxygen) for many hours, thereby, cross-linking the structureand “setting” the pitch so it does not melt during carbonization. SeeHagar, Joseph W. and Max L. Lake, “Formulation of a Mathematical ProcessModel Process Model for the Foaming of a Mesophase Carbon Precursor,Mat. Res. Soc. Symp., Materials Research Society, 270:35-40 (1992) andWhite, J. L., and P. M. Shaeffer, Carbon, 27:697 (1989). This is a timeconsuming step and can be an expensive step depending on the part sizeand equipment required. The “set” or oxidized pitch is then carbonizedin an inert atmosphere to temperatures as high as 1100° C. Then,graphitization is performed at temperatures as high as 3000° C. toproduce a high thermal conductivity graphitic structure, resulting in astiff and very thermally conductive foam.

Other techniques utilize a polymeric precursor, such as phenolic,urethane, or blends of these with pitch. See Hagar, Joseph W. and Max L.Lake, “Idealized Strut Geometries for Open-Celled Foams,” Mat. Res. Soc.Symp., Materials Research Society, 270:41-46 (1992), Aubert, J. W., (MRSSymposium Proceedings, 207:117-127 (1990), Cowlard, F. C. and J. C.Lewis, J. of Mat. Sci., 2:507-512 (1967) and Noda, T., Inagaki and S.Yamada, J. of Non-Crystalline Solids, 1:285-302, (1969). High pressureis applied and the sample is heated. At a specified temperature, thepressure is released, thus causing the liquid to foam as volatilecompounds are released. The polymeric precursors are cured and thencarbonized without a stabilization step. However, these precursorsproduce a “glassy” or vitreous carbon which does not exhibit graphiticstructure and, thus, has low thermal conductivity and low stiffness. SeeHagar, Joseph W. and Max L. Lake, “Idealized Strut Geometries forOpen-Celled Foams,” Mat. Res. Soc. Symp., Materials Research Society,270:41-46 (1992).

In either case, once the foam is formed, it is then bonded in a separatestep to the facesheet used in the composite. This can be an expensivestep in the utilization of the foam.

The process of this invention overcomes these limitations, by notrequiring a “blowing” or “pressure release” technique to produce thefoam. Furthermore, an oxidation stabilization step is not required, asin other methods used to produce pitch-based carbon foams with a highlyaligned graphitic structure. This process is less time consuming, andtherefore, will be lower in cost and easier to fabricate.

Lastly the foam can be produced with an integrated sheet of high thermalconductivity carbon on the surface of the foam, thereby producing acarbon foam with a smooth sheet on the surface to improve heat transfer.

SUMMARY OF THE INVENTION

The general object of the present invention is to provide carbon foamand a composite from a mesophase or isotropic pitch such as synthetic,petroleum or coal-tar based pitch.

Another object is to provide a carbon foam and a composite from pitchwhich does not require an oxidative stabilization step.

These and other objectives are accomplished by a method of producingcarbon foam wherein an appropriate mold shape is selected and preferablyan appropriate mold release agent is applied to walls of the mold. Pitchis introduced to an appropriate level in the mold, and the mold ispurged of air such as by applying a vacuum. Alternatively, an inertfluid could be employed. The pitch is heated to a temperature sufficientto coalesce the pitch into a liquid which preferably is of about 50° C.to about 100° C. above the softening point of the pitch. The vacuum isreleased and an inert fluid applied at a static pressure up to about1000 psi. The pitch is heated to a temperature sufficient to cause gasesto evolve and foam the pitch. The pitch is further heated to atemperature sufficient to coke the pitch and the pitch is cooled to roomtemperature with a simultaneous and gradual release of pressure.

In another aspect, the previously described steps are employed in a moldcomposed of a material such that the molten pitch does not wet.

In yet another aspect, the objectives are accomplished by the carbonfoam product produced by the methods disclosed herein including a foamproduct with a smooth integral facesheet.

In still another aspect a carbon foam composite product is produced byadhering facesheets to a carbon foam produced by the process of thisinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph illustrating typical carbon foam withinterconnected carbon ligaments and open porosity.

FIGS. 2-6 are micrographs of pitch-derived carbon foam graphitized at2500° C. and at various magnifications.

FIG. 7 is a SEM micrograph of the foam produced by the process of thisinvention.

FIG. 8 is a chart illustrating cumulative intrusion volume versus porediameter.

FIG. 9 is a chart illustrating log differential intrusion volume versuspore diameter.

FIG. 10 is a graph illustrating the temperatures at which volatiles aregiven off from raw pitch.

FIG. 11 is an X-ray analysis of the graphitized foam produced by theprocess of this invention.

FIGS. 12A-C are photographs illustrating foam produced with aluminumcrucibles and the smooth structure or face sheet that develops.

FIG. 13A is a schematic view illustrating the production of a carbonfoam composite made in accordance with this invention.

FIG. 13B is a perspective view of the carbon foam composite of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

In order to illustrate the carbon foam product and composite of thisinvention, the following Examples are set forth. They are not intendedto limit the invention in any way.

EXAMPLE I

Pitch powder, granules, or pellets are placed in a mold with the desiredfinal shape of the foam. These pitch materials can be solvated ifdesired. In this Example Mitsubishi ARA-24 mesophase pitch was utilized.A proper mold release agent or film is applied to the sides of the moldto allow removal of the part. In this case, Boron Nitride spray and DryGraphite Lubricant were separately used as a mold release agent. If themold is made from pure aluminum, no mold release agent is necessarysince the molten pitch does not wet the aluminum and, thus, will notstick to the mold. Similar mold materials may be found that the pitchdoes not wet and, thus, they will not need mold release. The sample isevacuated to less than 1 torr and then heated to a temperatureapproximately 50 to 100° C. above the softening point. In this casewhere Mitsubishi ARA24 mesophase pitch was used, 300° C. was sufficient.At this point, the vacuum is released to a nitrogen blanket and then apressure of up to 1000 psi is applied. The temperature of the system isthen raised to 800° C., or a temperature sufficient to coke the pitchwhich is 500° C. to 1000° C. This is performed at a rate of no greaterthan 5° C./min. and preferably at about 2° C./min. The temperature isheld for at least 15 minutes to achieve an assured soak and then thefurnace power is turned off and cooled to room temperature. Preferablythe foam was cooled at a rate of approximately 1.5° C./min. with releaseof pressure at a rate of approximately 2 psi/min. Final foamtemperatures for three product runs were 500° C., 630° C. and 800° C.During the cooling cycle, pressure is released gradually to atmosphericconditions. The foam was then heat treated to 1050° C. (carbonized)under a nitrogen blanket and then heat treated in separate runs to 2500°C. and 2800° C. (graphitized) in Argon.

Carbon foam produced with this technique was examined withphotomicrography, scanning electron microscopy (SEM), X-ray analysis,and mercury porisimetry. As can be seen in the FIGS. 2-7, theinterference patterns under cross-polarized light indicate that thestruts of the foam are completely graphitic. That is, all of the pitchwas converted to graphite and aligned along the axis of the struts.These struts are also similar in size and are interconnected throughoutthe foam. This would indicate that the foam would have high stiffnessand good strength. As seen in FIG. 7 by the SEM micrograph of the foam,the foam is open cellular meaning that the porosity is not closed. FIGS.8 and 9 are results of the mercury porisimetry tests. These testsindicate that the pore sizes are in the range of 90-200 microns.

A thermogravimetric study of the raw pitch was performed to determinethe temperature at which the volatiles are evolved. As can be seen inFIG. 11, the pitch loses nearly 20% of its mass fairly rapidly in thetemperature range between about 420° C. and about 480° C. Although thiswas performed at atmospheric pressure, the addition of 1000 psi pressurewill not shift this effect significantly. Therefore, while the pressureis at 1000 psi, gases rapidly evolved during heating through thetemperature range of 420° C. to 480° C. The gases produce a foamingeffect (like boiling) on the molten pitch. As the temperature isincreased further to temperatures ranging from 500° C. to 1000° C.(depending on the specific pitch), the foamed pitch becomes coked (orrigid), thus producing a solid foam derived from pitch. Hence, thefoaming has occurred before the release of pressure and, therefore, thisprocess is very different from previous art.

Samples from the foam were machined into specimens for measuring thethermal conductivity. The bulk thermal conductivity ranged from 58 W/m·Kto 106 W/m·K. The average density of the samples was 0.53 g/cm³. Whenweight is taken into account, the specific thermal conductivity of thepitch derived foam is over 4 times greater than that of copper. Furtherderivations can be utilized to estimate the thermal conductivity of thestruts themselves to be nearly 700 W/m·K. This is comparable to highthermal conductivity carbon fibers produced from this same ARA24mesophase pitch.

X-ray analysis of the foam was performed to determine the crystallinestructure of the material. The x-ray results are shown in FIG. 11. Fromthis data, the graphene layer spacing (d₀₀₂) was determined to be 0.336nm. The coherence length (La, 1010) was determined to be 203.3 nm andthe stacking height was determined to be 442.3 nm.

The compression strength of the samples were measured to be 3.4 MPa andthe compression modulus was measured to be 73.4 MPa. The foam sample waseasily machined and could be handled readily without fear of damage,indicating a good strength.

It is important to note that when this pitch is heated in a similarmanner, but under only atmospheric pressure, the pitch foamsdramatically more than when under pressure. In fact, the resulting foamis so fragile that it could not even be handled to perform tests.

EXAMPLE II

An alternative to the method of Example I is to utilize a mold made fromaluminum. In this case two molds were used, an aluminum weighing dishand a sectioned soda can. The same process as set forth in Example I isemployed except that the final coking temperature was only 630° C., soas to prevent the aluminum from melting.

FIGS. 12A-C illustrate the ability to utilized complex shaped molds forproducing complex shaped foam. In one case, shown in FIG. 12A the top ofa soda can was removed and the remaining can used as a mold. No releaseagent was utilized. Note that the shape of the resulting part conformsto the shape of the soda can, even after graphitization to 2800° C. Thisdemonstrates the dimensional stability of the foam and the ability toproduce near net shaped parts.

In the second case, as shown in FIGS. 12B and C employing an aluminumweight dish, a very smooth surface was formed on the surface contactingthe aluminum. This is directly attributable to the fact that the moltenpitch does not wet the surface of the aluminum. This would allow one toproduce complex shaped parts with smooth surfaces so as to improvecontact area for bonding or improving heat transfer. This smooth surfacewill act as a face sheet and, thus, a foam-core composite can befabricated in-situ with the fabrication of the face sheet. Since it isfabricated together and an integral material no interface joints result,thermal stresses will be less, resulting in a stronger material.

The following examples illustrate the production of a composite materialemploying the foam of this invention.

EXAMPLE III

Pitch derived carbon foam was produced with the method described inExample I. Referring to FIG. 13A the carbon foam 10 was then machinedinto a block 2″×2″×½″. Two pieces 12 and 14 of a prepeg comprised ofHercules AS4 carbon fibers and ICI Fibirite Polyetheretherkeytonethermoplastic resin also of 2″×2″×½″ size were placed on the top andbottom of the foam sample, and all was placed in a matched graphite mold16 for compression by graphite plunger 18. The composite sample washeated under an applied pressure of 100 psi to a temperature of 380° C.at a rate of 5° C./min. The composite was then heated under a pressureof 100 psi to a temperature of 650° C. The foam core sandwich panelgenerally 20 was then removed from the mold and carbonized undernitrogen to 1050° C. and then graphitized to 2800° C., resulting in afoam with carbon-carbon facesheets bonded to the surface. The compositegenerally 30 is shown in FIG. 13B.

EXAMPLE IV

Pitch derived carbon foam was produced with the method described inExample I. It was then machined into a block 2″×2″×½. Two pieces ofcarbon-carbon material, 2″×2″×½″, were were coated lightly with amixture of 50% ethanol, 50% phenolic Durez© Resin available fromOccidental Chemical Co. The foam block and carbon-carbon material werepositioned together and placed in a mold as indicated in Example III.The sample was heated to a temperature of 150° C. at a rate of 5° C./minand soaked at temperature for 14 hours. The sample was then carbonizedunder nitrogen to 1050° C. and then graphitized to 2800° C., resultingin a foam with carbon-carbon facesheets bonded to the surface. This isalso shown generally at 30 in FIG. 13B.

EXAMPLE V

Pitch derived carbon foam was produced with the method described inExample I. The foam sample was then densified with carbon by the methodof chemical vapor infiltration for 100 hours. The density increased to1.4 g/cm³, the flexural strength was 19.5 MPa and the flexural moduluswas 2300 MPa. The thermal conductivity of the raw foam was 58 W/m·K andthe thermal conductivity of the densified foam was 94 W/m·K.

EXAMPLE VI

Pitch derived carbon foam was produced with the method described inExample I. The foam sample was then densified with epoxy by the methodof vacuum impregnation. The epoxy was cured at 150° C. for 5 hours. Thedensity increased to 1.37 g/cm³ and the flexural strength was measuredto be 19.3 MPa.

It is obvious that other materials, such as metals, ceramics, plastics,or fiber reinforced plastics could be bonded to the surface of the foamof this invention to produce a foam core composite material withacceptable properties. It is also obvious that ceramics, or glass, orother materials could be impregnated into the foam for densification.

Based on the data taken to date from the carbon foam material, severalobservations can be made and the important features of the inventionare:

1. Pitch-based carbon foam can be produced without an oxidativestabilization step, thus saving time and costs.

2. High graphitic alignment in the struts of the foam is achieved upongraphitization to 2500° C., and thus high thermal conductivity andstiffness will be exhibited by the foam, making them suitable as a corematerial for thermal applications.

3. High compressive strengths should be achieved with mesophasepitch-based carbon foams, making them suitable as a core material forstructural applications.

4. Foam core composites can be fabricated at the same time as the foamis generated, thus saving time and costs.

5. Rigid monolithic preforms can be made with significant open porositysuitable for densification by the Chemical Vapor Infiltration method ofceramic and carbon infiltrants.

6. Rigid monolithic preforms can be made with significant open porositysuitable for activation, producing a monolithic activated carbon.

7. It is obvious that by varying the pressure applied, the size of thebubbles formed during the foaming will change and, thus, the density,strength, and other properties can be affected.

The following alternative procedures and products can also be effectedby the process of this invention:

1. Fabrication of preforms with complex shapes for densification by CVIor Melt Impregnation.

2. Activated carbon monoliths.

3. Optical absorbent.

4. Low density heating elements.

5. Firewall Material.

6. Low secondary electron emission targets for high-energy physicsapplications.

It will thus be seen that the present invention provides for themanufacture of pitch-based carbon foam for structural and thermalcomposites. The process involves the fabrication of a graphitic foamfrom a mesophase or isotropic pitch which can be synthetic, petroleum,or coal-tar based. A blend of these pitches can also be employed. Thesimplified process utilizes a high pressure high temperature furnace andthereby, does not require and oxidative stabilization step. The foam hasa relatively uniform distribution of pore sizes (≈100 microns), verylittle closed porosity, and density of approximately 0.53 g/cm³. Themesophase pitch is stretched along the struts of the foam structure andthereby produces a highly aligned graphitic structure in the struts.These struts will exhibit thermal conductivities and stiffness similarto the very expensive high performance carbon fibers (such as P-120 andK1100). Thus, the foam will exhibit high stiffness and thermalconductivity at a very low density (≈0.5 g/cc). This foam can be formedin place as a core material for high temperature sandwich panels forboth thermal and structural applications, thus reducing fabricationtime.

By utilizing an isotropic pitch, the resulting foam can be easilyactivated to produce a high surface area activated carbon. The activatedcarbon foam will not experience the problems associated with granulessuch as attrition, channeling, and large pressure drops.

What is claimed is:
 1. An essentially graphitic carbon foam having poresizes in the range of about 90 microns to about 200 microns produced bya process comprising: providing pitch in a container; heating said pitchin a non-oxidizing atmosphere at a pressure to a temperature sufficientto coalesce said pitch to form a liquid of said pitch; increasing saidpressure of said non-oxidizing atmosphere in said container containingsaid liquid of said pitch from said pressure to an increased pressurehaving a range greater than said pressure to about 1000 psi to form acarbon foam; heating said carbon foam in said non-oxidizing atmosphereto a temperature sufficient to carbonize said carbon foam to form acarbonized carbon foam; and heating said carbonized carbon foam to atemperature sufficient to form a thermal conducting essentiallygraphitic carbon foam having a bulk thermal conductivity of from 58W/m·K to about 106 W/m·K and a specific thermal conductivity greaterthan 100 W·cm³/m·K·g.
 2. An essentially graphitic carbon foam having abulk thermal conductivity/density greater than 100 W·cm³/m·K·g, producedby a process comprising: providing pitch in a container; heating saidpitch in a non-oxidizing atmosphere at a pressure to a temperaturesufficient to coalesce said pitch to form a liquid of said pitch;increasing said pressure of said non-oxidizing atmosphere in saidcontainer containing said liquid of said pitch from said pressure to anincreased pressure having a range greater than said pressure to about1000 psi to form a carbon foam; heating said carbon foam in saidnon-oxidizing atmosphere to a temperature sufficient to carbonize saidcarbon foam to form a carbonized carbon foam; and heating saidcarbonized carbon foam to a temperature sufficient to form a thermalconducting essentially graphitic carbon foam having a specific thermalconductivity greater than an essentially amorphous carbon foam.
 3. Anessentially graphitic carbon foam having a specific thermal conductivitygreater than copper.
 4. An essentially graphitic carbon foam having abulk thermal conductivity/density greater than 100 W·cm³/m·K·g.
 5. Anessentially graphitic carbon foam having a bulk thermal conductivity offrom 58 W/m·K to about 106 W/m·K and a specific thermal conductivitygreater than 100 W·cm³/m·K·g.
 6. An essentially graphitic carbon foam asdefined in claim 5 having pore sizes in the range of about 90 microns toabout 200 microns.
 7. An essentially graphitic carbon foam having a bulkthermal conductivity of at least 58 W/m·K and a specific thermalconductivity greater than 100 W·cm³/m·K·g.
 8. A carbon foam defined inclaim 7, said carbon foam having an open cell pore structure consistingessentially of substantially ellipsoidal pores, said carbon foam havingbeen derived from a pitch selected from the group consisting ofsynthetic mesophase pitch, synthetic isotropic pitch, petroleum-derivedmesophase pitch, petroleum-derived isotropic pitch, and coal-tar-derivedmesophase pitch.
 9. A carbon foam as defined in claim 7, said carbonfoam with an open cell pore structure substantially comprised of poreswhose planar cross sectional images are substantially circular orelliptical, said carbon foam having been derived from a pitch selectedfrom the group consisting of synthetic mesophase pitch, syntheticisotropic pitch, petroleum-derived mesophase pitch, petroleum-derivedisotropic pitch, and coal-tar-derived mesophase pitch.
 10. Anon-oxidatively stabilized, essentially graphitic carbon foam ofsubstantially open cell structure comprising cell walls wherein carbonderived from a mesophase pitch is in the form of graphite andsubstantially aligned along the cell wall axes.
 11. An essentiallygraphitic carbon foam as defined in claim 7 or 8, characterized by anX-ray diffraction pattern having an average d002 spacing of about 0.336nm.
 12. An essentially graphitic carbon foam as defined in claim 8, 9,or 10, having a bulk thermal conductivity from about 58 W/m·K to about106 W/m·K.
 13. An essentially graphitic carbon foam as defined in claim8, 9, or 10, having a specific thermal conductivity from about 109W·cm³/m·K·g to about 200 W·cm³/m·K·g.
 14. An essentially graphiticcarbon foam as defined in claim 8, 9, or 10, having a specific thermalconductivity greater than four times that of copper.
 15. An essentiallygraphitic carbon foam as defined in claim 8, 9, or 10, having a specificthermal conductivity greater than that of copper.
 16. An essentiallygraphitic carbon foam as defined in claim 8, 9, or 10, having a bulkthermal conductivity from about 58 W/m·K to about 106 W/m·K and beingcharacterized by an X-ray diffraction pattern substantially as depictedin FIG.
 11. 17. An essentially graphitic carbon foam as defined in claim8, 9, or 10, having a specific thermal conductivity of at least about109 W·cm³/m·K·g and being characterized by an X-ray diffraction patternexhibiting relatively sharp doublet peaks at 2θ angles between 40 and 50degrees.
 18. An essentially graphitic carbon foam as defined in claim 17wherein the X-ray diffraction pattern has an average d002 spacing of0.336 nm.
 19. An essentially graphitic carbon foam as defined in claim8, 9, or 10, having a specific thermal conductivity from about 109W·cm³/m·K·g to about 200 W·cm³/m·K·g and being characterized by an X-raydiffraction pattern having an average d002 spacing of about 0.336 nm.20. An essentially graphitic carbon foam as defined in claim 19 whereinthe X-ray diffraction pattern exhibits relatively sharp doublet peaks at2θ angles between 40 and 50 degrees.
 21. An essentially graphitic carbonfoam as defined in claim 8, 9, or 10, having a specific thermalconductivity greater than four times that of copper and beingcharacterized by an X-ray diffraction pattern having an average d002spacing of 0.336 nm.
 22. An essentially graphitic carbon foam as definedin claim 21 wherein the X-ray diffraction pattern exhibits relativelysharp doublet peaks at 2θ angles between 40 and 50 degrees.
 23. Anessentially graphitic carbon foam as defined in claim 8, 9, or 10,having a specific thermal conductivity greater than that of copper andbeing characterized by an X-ray diffraction pattern having an averaged002 spacing of 0.336 nm.
 24. A pitch-derived, non-oxidativelystabilized, essentially graphitic carbon foam, said foam having a bulkthermal conductivity of at least 58 W/m·K and a specific thermalconductivity greater than 100 W·cm³/m·K·g, said foam being furthercharacterized by an open cell pore structure substantially comprised ofellipsoidal pores and by graphite substantially aligned along the axesof the cell walls.
 25. A carbon foam as defined in claim 24, said foambeing a mesophase pitch-derived, non-oxidatively stabilized carbon foamcharacterized (1) by an open cell pore structure consisting essentiallyof pores whose planar cross sectional images are substantially circularor elliptical and (2) by carbon substantially aligned along the axes ofthe cell walls.
 26. An essentially graphitic carbon foam as defined inclaim 24 or 25 further characterized by a specific thermal conductivityof at least about 109 W·cm³/m·K·g and an X-ray diffraction patternhaving an average d002 spacing of 0.336 nm.
 27. An essentially graphiticcarbon foam as defined in claim 26 wherein the X-ray diffraction patternexhibits relatively sharp doublet peaks at 2θ angles between 40 and 50degrees.
 28. An essentially graphitic carbon foam as defined in claim 27derived from a pitch selected from the group consisting ofpetroleum-derived mesophase pitch and synthetic mesophase pitch.
 29. Anessentially graphitic carbon foam as defined in claim 27 wherein thespecific thermal conductivity is between about 109 and 200 W·cm³/m·K·g.30. An essentially graphitic carbon foam as defined in claim 29 derivedfrom a petroleum mesophase pitch.
 31. An essentially graphitic carbonfoam as defined in claim 24 or 25 further characterized by a specificthermal conductivity greater than copper and an X-ray diffractionpattern having an average d002 spacing of about 0.336 nm.
 32. Anessentially graphitic carbon foam as defined in claim 31 derived from apitch selected from the group consisting of petroleum-derived mesophasepitch, coal-tar-derived mesophase pitch, and synthetic mesophase pitch.33. An essentially graphitic carbon foam as defined in claim 24 or 25,further characterized by a specific thermal conductivity greater thanfour times that of copper and an X-ray diffraction pattern substantiallyas depicted in FIG. 11 and derived from a pitch selected from the groupconsisting of petroleum-derived mesophase pitch, coal-tar-derivedmesophase pitch, and synthetic mesophase pitch.
 34. An essentiallygraphitic carbon foam as defined in claim 24 or 25 having a bulk thermalconductivity from about 58 W/m·K to about 106 W/m·K and an X-raydiffraction pattern having an average d002 spacing of about 0.336 nm.35. An essentially graphitic carbon foam as defined in claim 34 derivedfrom a pitch selected from the group consisting of petroleum-derivedmesophase pitch and synthetic mesophase pitch.
 36. An essentiallygraphitic carbon foam as defined in claim 34 wherein the X-raydiffraction pattern exhibits relatively sharp doublet peaks at 2θ anglesbetween 40 and 50 degrees.
 37. An essentially graphitic carbon foam asdefined in claim 36 derived from a petroleum mesophase pitch.
 38. Anessentially graphitic carbon foam as defined in claim 3, 9 or 25 derivedfrom a petroleum mesophase pitch.
 39. An essentially graphitic carbonfoam as defined in claim 8 or 24 derived from a pitch selected from thegroup consisting of petroleum-derived mesophase pitch, coal-tar-derivedmesophase pitch, and synthetic mesophase pitch.
 40. A foam as defined inclaim 3, 7, 8, 9, 10, 24, or 25 having a pore structure consistingessentially of pores having diameters within a 100 micron range.
 41. Anessentially graphitic carbon foam having a bulk thermal conductivityfrom about 58 W/m·K to about 106 W/m·K and a specific thermalconductivity greater than 100 W·cm³/m·K·g, said foam characterized by anX-ray diffraction pattern having an average d002 spacing of about 0.336nm.
 42. An essentially graphitic carbon foam as defined in claim 8, 9 or10 having a specific thermal conductivity of at least 109 W·cm³/m·K·g.43. An essentially graphitic carbon foam as defined in claim 23 whereinthe X-ray diffraction pattern exhibits relatively sharp doublet peaks at2θ angles between 40 and 50 degrees.
 44. An essentially graphitic carbonfoam as defined in claim 26 derived from a pitch selected from the groupconsisting of petroleum-derived mesophase pitch, coal-tar-derivedmesophase pitch, and synthetic mesophase pitch.
 45. An essentiallygraphitic carbon foam as defined in claim 24 or 25 further characterizedby a specific thermal conductivity greater than four times that ofcopper and an X-ray diffraction pattern substantially as depicted inFIG.
 11. 46. An essentially graphitic carbon foam as defined in claim 7or 10 derived from a pitch selected from the group consisting ofpetroleum-derived mesophase pitch and synthetic mesophase pitch.